Copyright	(c) Harvard University 2008-2011 (c) Geoffrey Mainland 2011-2016
License	BSD-style
Maintainer	mainland@cs.drexel.edu
Safe Haskell	None
Language	Haskell98

Control.Monad.Exception

Description

Synopsis

class (Typeable e, Show e) => Exception e where
- toException :: e -> SomeException
- fromException :: SomeException -> Maybe e
- displayException :: e -> String
data SomeException
class Monad m => MonadException m where
- throw :: Exception e => e -> m a
- catch :: Exception e => m a -> (e -> m a) -> m a
- finally :: m a -> m b -> m a
onException :: MonadException m => m a -> m b -> m a
class (MonadIO m, MonadException m) => MonadAsyncException m where
- mask :: ((forall a. m a -> m a) -> m b) -> m b
bracket :: MonadAsyncException m => m a -> (a -> m b) -> (a -> m c) -> m c
bracket_ :: MonadAsyncException m => m a -> m b -> m c -> m c
newtype ExceptionT m a = ExceptionT {
- runExceptionT :: m (Either SomeException a)
}
mapExceptionT :: (m (Either SomeException a) -> n (Either SomeException b)) -> ExceptionT m a -> ExceptionT n b
liftException :: MonadException m => Either SomeException a -> m a

Documentation

class (Typeable e, Show e) => Exception e where #

Minimal complete definition

Nothing

Methods

toException :: e -> SomeException #

fromException :: SomeException -> Maybe e #

displayException :: e -> String #

Instances

Instances details

Exception NestedAtomically
Instance details Defined in Control.Exception.Base Methods toException :: NestedAtomically -> SomeException # fromException :: SomeException -> Maybe NestedAtomically # displayException :: NestedAtomically -> String #
Exception NoMethodError
Instance details Defined in Control.Exception.Base Methods toException :: NoMethodError -> SomeException # fromException :: SomeException -> Maybe NoMethodError # displayException :: NoMethodError -> String #
Exception NonTermination
Instance details Defined in Control.Exception.Base Methods toException :: NonTermination -> SomeException # fromException :: SomeException -> Maybe NonTermination # displayException :: NonTermination -> String #
Exception PatternMatchFail
Instance details Defined in Control.Exception.Base Methods toException :: PatternMatchFail -> SomeException # fromException :: SomeException -> Maybe PatternMatchFail # displayException :: PatternMatchFail -> String #
Exception RecConError
Instance details Defined in Control.Exception.Base Methods toException :: RecConError -> SomeException # fromException :: SomeException -> Maybe RecConError # displayException :: RecConError -> String #
Exception RecSelError
Instance details Defined in Control.Exception.Base Methods toException :: RecSelError -> SomeException # fromException :: SomeException -> Maybe RecSelError # displayException :: RecSelError -> String #
Exception RecUpdError
Instance details Defined in Control.Exception.Base Methods toException :: RecUpdError -> SomeException # fromException :: SomeException -> Maybe RecUpdError # displayException :: RecUpdError -> String #
Exception TypeError
Instance details Defined in Control.Exception.Base Methods toException :: TypeError -> SomeException # fromException :: SomeException -> Maybe TypeError # displayException :: TypeError -> String #
Exception ErrorCall
Instance details Defined in GHC.Exception Methods toException :: ErrorCall -> SomeException # fromException :: SomeException -> Maybe ErrorCall # displayException :: ErrorCall -> String #
Exception ArithException
Instance details Defined in GHC.Exception.Type Methods toException :: ArithException -> SomeException # fromException :: SomeException -> Maybe ArithException # displayException :: ArithException -> String #
Exception SomeException
Instance details Defined in GHC.Exception.Type Methods toException :: SomeException -> SomeException # fromException :: SomeException -> Maybe SomeException # displayException :: SomeException -> String #
Exception AllocationLimitExceeded
Instance details Defined in GHC.IO.Exception Methods toException :: AllocationLimitExceeded -> SomeException # fromException :: SomeException -> Maybe AllocationLimitExceeded # displayException :: AllocationLimitExceeded -> String #
Exception ArrayException
Instance details Defined in GHC.IO.Exception Methods toException :: ArrayException -> SomeException # fromException :: SomeException -> Maybe ArrayException # displayException :: ArrayException -> String #
Exception AssertionFailed
Instance details Defined in GHC.IO.Exception Methods toException :: AssertionFailed -> SomeException # fromException :: SomeException -> Maybe AssertionFailed # displayException :: AssertionFailed -> String #
Exception AsyncException
Instance details Defined in GHC.IO.Exception Methods toException :: AsyncException -> SomeException # fromException :: SomeException -> Maybe AsyncException # displayException :: AsyncException -> String #
Exception BlockedIndefinitelyOnMVar
Instance details Defined in GHC.IO.Exception Methods toException :: BlockedIndefinitelyOnMVar -> SomeException # fromException :: SomeException -> Maybe BlockedIndefinitelyOnMVar # displayException :: BlockedIndefinitelyOnMVar -> String #
Exception BlockedIndefinitelyOnSTM
Instance details Defined in GHC.IO.Exception Methods toException :: BlockedIndefinitelyOnSTM -> SomeException # fromException :: SomeException -> Maybe BlockedIndefinitelyOnSTM # displayException :: BlockedIndefinitelyOnSTM -> String #
Exception CompactionFailed
Instance details Defined in GHC.IO.Exception Methods toException :: CompactionFailed -> SomeException # fromException :: SomeException -> Maybe CompactionFailed # displayException :: CompactionFailed -> String #
Exception Deadlock
Instance details Defined in GHC.IO.Exception Methods toException :: Deadlock -> SomeException # fromException :: SomeException -> Maybe Deadlock # displayException :: Deadlock -> String #
Exception IOException
Instance details Defined in GHC.IO.Exception Methods toException :: IOException -> SomeException # fromException :: SomeException -> Maybe IOException # displayException :: IOException -> String #
Exception SomeAsyncException
Instance details Defined in GHC.IO.Exception Methods toException :: SomeAsyncException -> SomeException # fromException :: SomeException -> Maybe SomeAsyncException # displayException :: SomeAsyncException -> String #
Exception ExitCode
Instance details Defined in GHC.IO.Exception Methods toException :: ExitCode -> SomeException # fromException :: SomeException -> Maybe ExitCode # displayException :: ExitCode -> String #
Exception FixIOException
Instance details Defined in GHC.IO.Exception Methods toException :: FixIOException -> SomeException # fromException :: SomeException -> Maybe FixIOException # displayException :: FixIOException -> String #

data SomeException #

Instances

Instances details

Show SomeException
Instance details Defined in GHC.Exception.Type Methods showsPrec :: Int -> SomeException -> ShowS show :: SomeException -> String showList :: [SomeException] -> ShowS
Exception SomeException
Instance details Defined in GHC.Exception.Type Methods toException :: SomeException -> SomeException # fromException :: SomeException -> Maybe SomeException # displayException :: SomeException -> String #

class Monad m => MonadException m where Source #

Minimal complete definition

throw, catch

Methods

throw :: Exception e => e -> m a Source #

Throw an exception.

catch Source #

Arguments

:: Exception e
=> m a	The computation to run
-> (e -> m a)	Handler to invoke if an exception is raised
-> m a

Catch an exception.

finally Source #

Arguments

:: m a	The computation to run
-> m b	Computation to run afterward (even if an exception was raised)
-> m a

Run a computation and always perform a second, final computation even if an exception is raised. If a short-circuiting monad transformer such as ErrorT or MaybeT is used to transform a MonadException monad, then the implementation of finally for the transformed monad must guarantee that the final action is also always performed when any short-circuiting occurs.

Instances

Instances details

MonadException IO Source #
Instance details Defined in Control.Monad.Exception Methods throw :: Exception e => e -> IO a Source # catch :: Exception e => IO a -> (e -> IO a) -> IO a Source # finally :: IO a -> IO b -> IO a Source #
MonadException STM Source #
Instance details Defined in Control.Monad.Exception Methods throw :: Exception e => e -> STM a Source # catch :: Exception e => STM a -> (e -> STM a) -> STM a Source # finally :: STM a -> STM b -> STM a Source #
MonadException m => MonadException (ListT m) Source #
Instance details Defined in Control.Monad.Exception Methods throw :: Exception e => e -> ListT m a Source # catch :: Exception e => ListT m a -> (e -> ListT m a) -> ListT m a Source # finally :: ListT m a -> ListT m b -> ListT m a Source #
MonadException m => MonadException (MaybeT m) Source #
Instance details Defined in Control.Monad.Exception Methods throw :: Exception e => e -> MaybeT m a Source # catch :: Exception e => MaybeT m a -> (e -> MaybeT m a) -> MaybeT m a Source # finally :: MaybeT m a -> MaybeT m b -> MaybeT m a Source #
Monad m => MonadException (ExceptionT m) Source #
Instance details Defined in Control.Monad.Exception Methods throw :: Exception e => e -> ExceptionT m a Source # catch :: Exception e => ExceptionT m a -> (e -> ExceptionT m a) -> ExceptionT m a Source # finally :: ExceptionT m a -> ExceptionT m b -> ExceptionT m a Source #
(MonadException m, Error e) => MonadException (ErrorT e m) Source #
Instance details Defined in Control.Monad.Exception Methods throw :: Exception e0 => e0 -> ErrorT e m a Source # catch :: Exception e0 => ErrorT e m a -> (e0 -> ErrorT e m a) -> ErrorT e m a Source # finally :: ErrorT e m a -> ErrorT e m b -> ErrorT e m a Source #
MonadException m => MonadException (ExceptT e' m) Source #
Instance details Defined in Control.Monad.Exception Methods throw :: Exception e => e -> ExceptT e' m a Source # catch :: Exception e => ExceptT e' m a -> (e -> ExceptT e' m a) -> ExceptT e' m a Source # finally :: ExceptT e' m a -> ExceptT e' m b -> ExceptT e' m a Source #
MonadException m => MonadException (IdentityT m) Source #
Instance details Defined in Control.Monad.Exception Methods throw :: Exception e => e -> IdentityT m a Source # catch :: Exception e => IdentityT m a -> (e -> IdentityT m a) -> IdentityT m a Source # finally :: IdentityT m a -> IdentityT m b -> IdentityT m a Source #
MonadException m => MonadException (ReaderT r m) Source #
Instance details Defined in Control.Monad.Exception Methods throw :: Exception e => e -> ReaderT r m a Source # catch :: Exception e => ReaderT r m a -> (e -> ReaderT r m a) -> ReaderT r m a Source # finally :: ReaderT r m a -> ReaderT r m b -> ReaderT r m a Source #
MonadException m => MonadException (StateT s m) Source #
Instance details Defined in Control.Monad.Exception Methods throw :: Exception e => e -> StateT s m a Source # catch :: Exception e => StateT s m a -> (e -> StateT s m a) -> StateT s m a Source # finally :: StateT s m a -> StateT s m b -> StateT s m a Source #
MonadException m => MonadException (StateT s m) Source #
Instance details Defined in Control.Monad.Exception Methods throw :: Exception e => e -> StateT s m a Source # catch :: Exception e => StateT s m a -> (e -> StateT s m a) -> StateT s m a Source # finally :: StateT s m a -> StateT s m b -> StateT s m a Source #
(Monoid w, MonadException m) => MonadException (WriterT w m) Source #
Instance details Defined in Control.Monad.Exception Methods throw :: Exception e => e -> WriterT w m a Source # catch :: Exception e => WriterT w m a -> (e -> WriterT w m a) -> WriterT w m a Source # finally :: WriterT w m a -> WriterT w m b -> WriterT w m a Source #
(Monoid w, MonadException m) => MonadException (WriterT w m) Source #
Instance details Defined in Control.Monad.Exception Methods throw :: Exception e => e -> WriterT w m a Source # catch :: Exception e => WriterT w m a -> (e -> WriterT w m a) -> WriterT w m a Source # finally :: WriterT w m a -> WriterT w m b -> WriterT w m a Source #
(Monoid w, MonadException m) => MonadException (RWST r w s m) Source #
Instance details Defined in Control.Monad.Exception Methods throw :: Exception e => e -> RWST r w s m a Source # catch :: Exception e => RWST r w s m a -> (e -> RWST r w s m a) -> RWST r w s m a Source # finally :: RWST r w s m a -> RWST r w s m b -> RWST r w s m a Source #
(Monoid w, MonadException m) => MonadException (RWST r w s m) Source #
Instance details Defined in Control.Monad.Exception Methods throw :: Exception e => e -> RWST r w s m a Source # catch :: Exception e => RWST r w s m a -> (e -> RWST r w s m a) -> RWST r w s m a Source # finally :: RWST r w s m a -> RWST r w s m b -> RWST r w s m a Source #

onException Source #

Arguments

:: MonadException m
=> m a	The computation to run
-> m b	Computation to run if an exception is raised
-> m a

If an exception is raised by the computation, then perform a final action and re-raise the exception.

class (MonadIO m, MonadException m) => MonadAsyncException m where Source #

Methods

mask :: ((forall a. m a -> m a) -> m b) -> m b Source #

Executes a computation with asynchronous exceptions masked. The argument passed to mask is a function that takes as its argument another function, which can be used to restore the prevailing masking state within the context of the masked computation.

Instances

Instances details

MonadAsyncException IO Source #
Instance details Defined in Control.Monad.Exception Methods mask :: ((forall a. IO a -> IO a) -> IO b) -> IO b Source #
MonadAsyncException m => MonadAsyncException (ListT m) Source #
Instance details Defined in Control.Monad.Exception Methods mask :: ((forall a. ListT m a -> ListT m a) -> ListT m b) -> ListT m b Source #
MonadAsyncException m => MonadAsyncException (MaybeT m) Source #
Instance details Defined in Control.Monad.Exception Methods mask :: ((forall a. MaybeT m a -> MaybeT m a) -> MaybeT m b) -> MaybeT m b Source #
MonadAsyncException m => MonadAsyncException (ExceptionT m) Source #
Instance details Defined in Control.Monad.Exception Methods mask :: ((forall a. ExceptionT m a -> ExceptionT m a) -> ExceptionT m b) -> ExceptionT m b Source #
(MonadAsyncException m, Error e) => MonadAsyncException (ErrorT e m) Source #
Instance details Defined in Control.Monad.Exception Methods mask :: ((forall a. ErrorT e m a -> ErrorT e m a) -> ErrorT e m b) -> ErrorT e m b Source #
MonadAsyncException m => MonadAsyncException (ExceptT e' m) Source #
Instance details Defined in Control.Monad.Exception Methods mask :: ((forall a. ExceptT e' m a -> ExceptT e' m a) -> ExceptT e' m b) -> ExceptT e' m b Source #
MonadAsyncException m => MonadAsyncException (IdentityT m) Source #
Instance details Defined in Control.Monad.Exception Methods mask :: ((forall a. IdentityT m a -> IdentityT m a) -> IdentityT m b) -> IdentityT m b Source #
MonadAsyncException m => MonadAsyncException (ReaderT r m) Source #
Instance details Defined in Control.Monad.Exception Methods mask :: ((forall a. ReaderT r m a -> ReaderT r m a) -> ReaderT r m b) -> ReaderT r m b Source #
MonadAsyncException m => MonadAsyncException (StateT s m) Source #
Instance details Defined in Control.Monad.Exception Methods mask :: ((forall a. StateT s m a -> StateT s m a) -> StateT s m b) -> StateT s m b Source #
MonadAsyncException m => MonadAsyncException (StateT s m) Source #
Instance details Defined in Control.Monad.Exception Methods mask :: ((forall a. StateT s m a -> StateT s m a) -> StateT s m b) -> StateT s m b Source #
(Monoid w, MonadAsyncException m) => MonadAsyncException (WriterT w m) Source #
Instance details Defined in Control.Monad.Exception Methods mask :: ((forall a. WriterT w m a -> WriterT w m a) -> WriterT w m b) -> WriterT w m b Source #
(Monoid w, MonadAsyncException m) => MonadAsyncException (WriterT w m) Source #
Instance details Defined in Control.Monad.Exception Methods mask :: ((forall a. WriterT w m a -> WriterT w m a) -> WriterT w m b) -> WriterT w m b Source #
(Monoid w, MonadAsyncException m) => MonadAsyncException (RWST r w s m) Source #
Instance details Defined in Control.Monad.Exception Methods mask :: ((forall a. RWST r w s m a -> RWST r w s m a) -> RWST r w s m b) -> RWST r w s m b Source #
(Monoid w, MonadAsyncException m) => MonadAsyncException (RWST r w s m) Source #
Instance details Defined in Control.Monad.Exception Methods mask :: ((forall a. RWST r w s m a -> RWST r w s m a) -> RWST r w s m b) -> RWST r w s m b Source #

bracket Source #

Arguments

:: MonadAsyncException m
=> m a	computation to run first ("acquire resource")
-> (a -> m b)	computation to run last ("release resource")
-> (a -> m c)	computation to run in-between
-> m c

When you want to acquire a resource, do some work with it, and then release the resource, it is a good idea to use bracket, because bracket will install the necessary exception handler to release the resource in the event that an exception is raised during the computation. If an exception is raised, then bracket will re-raise the exception (after performing the release).

bracket_ :: MonadAsyncException m => m a -> m b -> m c -> m c Source #

A variant of bracket where the return value from the first computation is not required.

newtype ExceptionT m a Source #

Constructors

ExceptionT
Fields runExceptionT :: m (Either SomeException a)

Instances

Instances details

MonadTrans ExceptionT Source #
Instance details Defined in Control.Monad.Exception Methods lift :: Monad m => m a -> ExceptionT m a
Monad m => Monad (ExceptionT m) Source #
Instance details Defined in Control.Monad.Exception Methods (>>=) :: ExceptionT m a -> (a -> ExceptionT m b) -> ExceptionT m b (>>) :: ExceptionT m a -> ExceptionT m b -> ExceptionT m b return :: a -> ExceptionT m a
Functor m => Functor (ExceptionT m) Source #
Instance details Defined in Control.Monad.Exception Methods fmap :: (a -> b) -> ExceptionT m a -> ExceptionT m b (<$) :: a -> ExceptionT m b -> ExceptionT m a
MonadFix m => MonadFix (ExceptionT m) Source #
Instance details Defined in Control.Monad.Exception Methods mfix :: (a -> ExceptionT m a) -> ExceptionT m a
Monad m => MonadFail (ExceptionT m) Source #
Instance details Defined in Control.Monad.Exception Methods fail :: String -> ExceptionT m a
(Functor m, Monad m) => Applicative (ExceptionT m) Source #
Instance details Defined in Control.Monad.Exception Methods pure :: a -> ExceptionT m a (<>) :: ExceptionT m (a -> b) -> ExceptionT m a -> ExceptionT m b liftA2 :: (a -> b -> c) -> ExceptionT m a -> ExceptionT m b -> ExceptionT m c (>) :: ExceptionT m a -> ExceptionT m b -> ExceptionT m b (<*) :: ExceptionT m a -> ExceptionT m b -> ExceptionT m a
(Functor m, Monad m) => Alternative (ExceptionT m) Source #
Instance details Defined in Control.Monad.Exception Methods empty :: ExceptionT m a (<\|>) :: ExceptionT m a -> ExceptionT m a -> ExceptionT m a some :: ExceptionT m a -> ExceptionT m [a] many :: ExceptionT m a -> ExceptionT m [a]
Monad m => MonadPlus (ExceptionT m) Source #
Instance details Defined in Control.Monad.Exception Methods mzero :: ExceptionT m a mplus :: ExceptionT m a -> ExceptionT m a -> ExceptionT m a
MonadIO m => MonadIO (ExceptionT m) Source #
Instance details Defined in Control.Monad.Exception Methods liftIO :: IO a -> ExceptionT m a
MonadAsyncException m => MonadAsyncException (ExceptionT m) Source #
Instance details Defined in Control.Monad.Exception Methods mask :: ((forall a. ExceptionT m a -> ExceptionT m a) -> ExceptionT m b) -> ExceptionT m b Source #
Monad m => MonadException (ExceptionT m) Source #
Instance details Defined in Control.Monad.Exception Methods throw :: Exception e => e -> ExceptionT m a Source # catch :: Exception e => ExceptionT m a -> (e -> ExceptionT m a) -> ExceptionT m a Source # finally :: ExceptionT m a -> ExceptionT m b -> ExceptionT m a Source #

mapExceptionT :: (m (Either SomeException a) -> n (Either SomeException b)) -> ExceptionT m a -> ExceptionT n b Source #

liftException :: MonadException m => Either SomeException a -> m a Source #

Lift the result of running a computation in a monad transformed by ExceptionT into another monad that supports exceptions.